With the continuous improvement in the quality of life, higher requirements for display technologies have been put forward. 3D, stereoscopic technology is one of the most important trends in current development of display technologies.
Currently, there are the following categories of stereoscopic technology.
Dual-color glasses based method:
In this method, a scene to be displayed on the screen is filtered with a driver program. Specifically, the image intended for the left eye is filtered to remove red, and the image intended for the right eye is filtered to remove cyan (blue and green). The viewer wears a pair of dual-color glasses. A filter lens over the left eye blocks red, and a filter lens over the right eye blocks cyan. Therefore, the left eye sees only the image intended for the left eye, and the right eye sees only the image intended for the right eye. The brain fuses both images into perception of regular colors. This is the lowest cost method of stereoscopic technology, but it is generally only suitable for scenes where color is not an important factor. As to other types of scenes, it may cause discomfort of viewers and severe color distortion due to the loss of color information.
Active stereoscopic method:
In this method, a driver program alternately transmits left eye and right eye images, for example, a left eye image at a first frame, a right eye image at a second frame, another left eye image at a third frame, and so forth. The viewer wears a pair of shutter glasses in synchronization with the display device in a wired or wireless manner. While presenting the left eye image, the display device opens the shutter in the left glass and closes the shutter in the right glass. While presenting the right eye image, the display device opens the shutter in the right glass and closes the shutter in the left glass. According to the phenomenon of persistence of vision, an afterimage is thought to persist in front of the eye whose view is blocked, and any viewer within the range can see a three-dimensional scene wearing a pair of the stereoscopic glasses. Generally, the shutters in the glasses are implemented with liquid crystals. The liquid crystal layer can be switched between transparent and dark by an applied electrical signal. This method reduces the brightness of the image in half, and has certain frequency requirements on the refresh rates of the display device and the shutters in the glasses, demanding more on the properties of the display device and the glasses, and resulting in higher manufacturing cost. Moreover, flicker caused by the frequent switching of the stereoscopic glasses is displeasing to the eye, and may tire the viewer.
Passive synchronization stereoscopic method:
In this method, a driver program simultaneously outputs left eye and right eye images. The left eye and right eye images are projected using two projectors. A polarizing filter is provided in front of the projector for the left eye image, and an orthogonal polarizing filter is provided in front of the projector for the right eye image. The viewer wears a pair of glasses, which also contain a pair of polarizing filters oriented the same as the projectors. According to the polarizing effect, each eye only sees the image intended for the eye itself. Currently, this is the stereoscopic method producing the best imaging results. However, since light emitted from the projector light source is like natural light, the polarizing filters on the outputs of the projectors cost 50% of the light energy, reducing the utilization rate of the light energy. Moreover, the use of two projection subsystems is costly, requires a large space and may cause inconvenience in installation and moving.
Due to its advantages such as wide color gamut and low energy consumption, laser-based display technology is considered one of the prominent, next generation display technologies. Combining laser-based display with stereoscopic projection is the current trend, one implementation of which is an active stereoscopic method. The screen alternately presents left eye and right eye images at twice the frequency, and the glasses dynamically block one of the eyes. That is, present the left eye image while blocking the right eye's view, and present the right eye image while blocking the left eye's view, so that the eyes are provided with different images, which are fused by the brain into perception of a three-dimensional scene. Multi-color display makes use of time-domain control, e.g., lights of different wavelengths are transmitted during different time slots according to a color wheel. Since each wavelength is illuminated separately during one time slot, the utilization rate of the laser light source is low. Moreover, the existing stereoscopic projection method includes two projection subsystems, one for projecting the left eye image and the other for projecting the right eye image, therefore, the size of the projection system is large, installation and moving inconvenience may be caused, and manufacturing and production costs are high. Furthermore, each of the left eye and right eye images uses only half of the light energy output from the laser, resulting in a low brightness of the image.